The constant threat of diminishing sources of fossil fuels and the resulting increases in prices for such fuels, coupled with the federally mandated requirements for reducing the amount of toxic emissions spewed into the atmosphere, has resulted in a great deal of interest in improving fuel economy, particularly the fuel economy of automobile combustion engines.
Such interest has led to the discovery of cleaner burning compositions, as well as to the discovery of a variety of fuel and/or engine lubricating oils compositions which result in improved fuel economy, i.e., a higher number of miles obtained in a given vehicle per U.S. gallon of fuel.
One such discovery, which is described in U.S. Pat. No. 4,584,112, involves lubricating the crankcase of an internal combustion engine with a lubricating oil composition consisting essentially of a hydrocarbon oil of lubricating viscosity, from 15 to 25 millimoles per kilogram of zinc O,O-di(2-ethylhexyl) phosphorodithioate, and from 0.25 to 2 wt. % of pentaerythritol monooleate.
U.S. Pat. No. 4,492,640 and U.S. Pat. No. 4,492,642 also describe methods for reducing the fuel consumption in internal combustion systems. Both of these patents described the addition to lubricating and/or fuel compositions used in an internal combustion engine of a friction reducing compound. The friction reducing compound disclosed in U.S. Pat. No. 4,492,640 comprises a boron derivative of a mixture of alkoxylated alcohols and hydroxyl sulfides, whereas the friction reducing compound disclosed in U.S. Pat. No. 4,492,642 comprises the product formed by reacting a borating agent with an ammoniated hydrocarbyl epoxide.
U.S. Pat. No. 4512903 discloses lubricating compositions which contain still other friction reducing compounds, namely, amides prepared from mono- or polyhydroxy substituted aliphatic monocarboxylic acids and primary or secondary amines.
U.S. Pat. No. 5,282,990 discloses a crankcase lubricating oil composition comprising an oil of lubricating viscosity and a synergistic blend of at least one compound (A) prepared by reaction an acid or a mixture of acids with a polyamine and at least one compound (B) prepared by reacting an acid or a mixture of acids with a polyol. That is, U.S. Pat. No. 528,990 generally discloses a lubricant additive concentrate comprising a lubricant oil and a synergistic blend of amine/amide and ester/alcohol friction modifying agents. This synergistic blend of friction modifying agents aids in the reduction of fuel consumption in an internal combustion engine.
Fuel economy improvement is a major driver in the performance of top of the line engine oils. At a given viscosity, changes in basestock composition can provide differences in fuel economy as measured by such tests as the Ford Sigma test and the M 111 test.
Engine oil manufacturers are attempting to change over by the year 2000 from engine oils which meet the ILSAC GF-2 specifications to a yet to be fully defined ILSAC GF-3 specification in order to reduce emissions, improve control system hardware protection, improve fuel economy and provide protection for extended drain intervals.
Lubricants in commercial use today are prepared from a variety of natural and synthetic basestocks admixed with various additive packages and solvents depending upon their intended application. Additive packages which include friction modifiers greatly affect the final cost and performance of the fully formulated lubricant. Therefore, it would be highly desirable to develop a lubricating oil for use in internal combustion engines which has a reduced level of additives, but provides the same or better fuel economy as lubricants with conventional amounts of such additives.
Lubricant basestocks used in internal combustion engine applications typically include mineral oils, highly refined mineral oils, polyalphaolefins (PAO), polyalkylene glycols (PAG), phosphate esters, silicone oils, diesters or polyol esters.
Synthetic lubricants provide a valuable alternative to natural lubricants (e.g., rapeseed oils, canola oils and sunflower oils) in a wide variety of applications. A preferred synthetic lubricant is neopolyol esters which are formed from the esterification of neopolyols and monocarboxylic acids. Thus, for example, use of neopolyols such as neopentyl glycol, trimethylolethane, trimethylolpropane, monopentaerythritol, technical grade pentaerythritol, dipentaerythritol, tripentaerythritol and the like can be esterified with carboxylic acids ranging from formic acid, acetic acid, propionic acid, up through long chain carboxylic acids both linear and branched. Typically, the acids employed range from C.sub.5 to C.sub.22.
One typical method of production of polyol esters would be to react a neopolyol with a carboxylic acid at elevated temperatures in the presence or absence of an added catalyst. Catalysts such as sulfuric acid, p-toluene sulfonic acid, phosphorous acid, and soluble metal esterification catalysts are conventionally employed.
While the method of production of neopolyol esters as outlined above is well known, the method produces materials with a set of standard properties. For a given combination of neopolyol and acid (or mixtures thereof) there is a set of product properties such as viscosity, viscosity index, molecular weight, pour point, flash point, thermal and oxidative stability, polarity, and biodegradability which are inherent to the compositions formed by the components in the recipe. To get out of the box of viscosity and other properties imposed by structure, attempts have been made to increase the viscosity of neopolyol esters by means of a second acid, a polybasic acid, in addition to, or instead of, the monocarboxylic acids described above. Thus, employing a polybasic acid such as, e.g., adipic acid, sebacic acid, azelaic acid and/or acid anhydrides such as, succinic, maleic and phthalic anhydride and the like enables one to have the components of a polymeric system when reacted with a neopolyol. By adding a poly- or di-basic acid to the mix, one is able to achieve some degree of cross-linking or oligomerization, thereby causing molecular size growth such that the overall viscosity of the system is increased. Higher viscosity oils are desirable in certain end use application such as greases, heavy duty engine oils, certain hydraulic fluids and the like.
Other conventional natural and synthetic esters may each provide one or more of the desired attributes, e.g., high viscosity, good low temperature properties, biodegradability, lubricity, seal compatibility, low toxicity, and good thermal and oxidative stability, but none appears to be able to meet all of the product attributes by themselves. Similarly, the natural basestocks such as rapeseed oil are capable of meeting the biodegradability and toxicity properties, but fail to meet the required high viscosity, lubricity, and thermal and oxidative stability properties. Moreover, none of the conventional engine lubricating oils discussed above appear to positively affect the percent fuel economy improvement such that the lubricant will meet or exceed the proposed GF-3 specifications. In order for the conventional lubricating oils to at least meet the proposed GF-3 specification, it will be required to increase the levels of various additives, such as friction modifiers and molybdenum, at a substantial increase in cost to the manufacturer.
The blended lubricant basestocks according to the present invention comprising a complex alcohol ester and at least one additional natural or synthetic basestock appears to satisfy all of the desired attributes for fully formulated lubricant basestocks by providing the basestock with effective lubricating properties such that it meets or exceeds the proposed lubricant GF-3 specifications, while substantially increasing the percent fuel economy improvement. They also provide excellent thermal and oxidative stability, good low temperature properties (i.e., low pour points), low toxicity, low volatility, and good seal compatibility.
The present inventors believe that the use of the unique complex alcohol ester basestocks together with conventional natural, hydrocarbon-based and/or other synthetic oil basestocks in lubricating internal combustion engines results in dramatically increased percent fuel economy improvements, while meeting or exceeding all of the viscosity and volatility requirements of the proposed GF-3 specification, is due to the fact that the complex alcohol ester basestock of the present invention is more likely than natural, hydrocarbon-based and/or other synthetic oils to find its way to the surface. Since the complex alcohol ester is a stable fluid at the surface, it is able to provide protection from metal-to-metal contact which manifests itself in the form of friction metal wear and heat loss. This friction metal wear contributes to reduced fuel economy. Solubility of mogas components in the lubricant leads to unburned fuel and higher emissions. The polarity of the unique complex alcohol ester compositions according to the present invention is such that less hydrocarbon is trapped in the oil, thereby reducing emissions.
Moreover, the complex alcohol esters of the present invention eliminate the necessity of adding costly molybdenum to the lubricating oil in order to satisfy the percent fuel economy improvement which is required under the proposed GF-3 specifications. To the contrary, if conventional molybdenum additives are added to the lubricating oil comprising complex alcohol esters the data set forth herein clearly demonstrates that the resulting product has reduced percent fuel economy improvement than lubricating oils using complex alcohol esters or molybdenum alone. It is believed that the molybdenum and complex alcohol esters compete for surface cites, thus reducing the effect on the friction and wear performance of the lubricating oil.
The complex alcohol esters with low polybasic acid ester content according to the present invention are formed by using no more than 20% excess alcohol during the reaction step. Furthermore, the present inventors have discovered that these unique complex alcohol esters according to the present invention can also be formed such that they have low metals and acid content by treating the crude reactor product with water at elevated temperatures and pressures greater than one atmosphere. That is, the present inventors have unexpectedly discovered that high temperature hydrolysis can be used to remove a substantial portion of the metal catalyst from the complex alcohol ester reaction product without any significant increase in the total acid number of the resulting product. Low metals and low acid number are important because both can catalyze the hydrolysis of the ester during end-use.
Moreover, the present inventors have also demonstrated that an unexpected, synergistic effect occurs when these complex alcohol esters of the present invention are blended with either a natural, hydrocarbon-based or synthetic ester basestock, i.e., the blended basestock unexpectedly exhibits enhanced product attributes versus either the complex alcohol ester or other basestock by itself. Thus, the blended basestocks according to the present invention exhibit the following attributes: percent fuel economy improvement, excellent lubricity, seal compatibility, low toxicity, good thermal and oxidative stability, a wide viscosity range to meet various iso grade needs, and improved engine performance.